Macro- and Microspectroscopic Study of Nd (III) Uptake Mechanisms in Hardened Cement Paste

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• 作者：Peter Mandaliev ; Rainer Dhn ; Bernhard Wehrli ; Erich Wieland
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：November 1, 2009
• 年：2009
• 卷：43
• 期：21
• 页码：8462-8468
• 全文大小：332K
• 年卷期：v.43,no.21(November 1, 2009)
• ISSN：1520-5851

文摘

Cement is an important component in repositories for low-level and intermediate-level radioactive waste. Nd uptake by hardened cement paste (HCP) has been investigated with the aim of developing a mechanistic understanding of the immobilization processes of trivalent lanthanides and actinides in HCP on the molecular level. Information on the microstructure of HCP, the Nd distribution in the cement matrix, and the coordination environment of Nd in these matrices was gained from the combined use of scanning electron microscopy (SEM), synchrotron-based μ-X-ray fluorescence (μ-XRF), μ-X-ray (μ-XAS), and bulk-X-ray absorption spectroscopy (bulk-XAS) on Nd doped cement samples. The samples were reacted over periods of time between 15 min and 200 days. SEM and μ-XRF investigations suggest preferential Nd accumulation in rims around “inner”-calcium silicate hydrates (C−S−H). The EXAFS data indicate that the coordination environment of Nd taken up by HCP was dependent on reaction time. Changes in the structural parameters derived from EXAFS support the idea of Nd incorporation into the structure of C−S−H phases. The Nd binding mechanisms proposed in this study have implication for an overall assessment of the safe disposal of trivalent actinides in cement-based repositories for radioactive waste.